We cover the benefits of PGS, and their magnitude. We dissect the subject of mosaicism and how it helps to construct a hierarchy of which embryos to transfer. We train patients to ask the relevant questions of their clinic, clinic’s laboratory, and reference laboratory before signing on to do PGS. Finally, we address the risk around damage during biopsy, how often useful embryos are being discarded, and how the investment in PGS looks for women of different ages.